This invention relates to a coil device such as a transformer or a choke coil used in an inverter circuit or the like and, in particular, to a low-profile coil device which includes a bobbin structure and coils wrapped around the bobbin structure.
Coil devices are generally grouped into two types: vertical type and horizontal type. A coil device of the vertical type has coils which are arranged so that their coil axes extend vertically. Another coil device of the horizontal type has coils which are arranged so that their coil axes extend horizontally. Recently, coil devices are required to have a low-profile with more coils. In view of the requirement, the horizontal-type coil device has advantages in its characteristics in comparison with the vertical-type coil device. For example, one of the horizontal-type coil devices is disclosed in JP-A 2005-72261, the contents of which are incorporated herein by reference.
As disclosed in JP-A 2005-72261, a normal coil device of the horizontal type has two pin lines, each of which consists of multiple pins or terminals. If the number of coils increases, each of the pin lines must be longer. The longer pin lines lose the size balance of the coil device.
In order to solve the above-mentioned size balance problem, JP-A 2004-260089 proposes a coil device of horizontal type that has four pin lines, the contents of JP-A 2004-260089 being incorporated herein by reference. However, the coil device of JP-A 2004-260089 has a complex structured coil bobbin formed with a plurality of holes which pierces its flange portions along a direction parallel with its coil axes. Because of the piercing holes, the complex structured coil bobbin is difficult to mold and does not have its adequate strength. JP-A 2000-150258 and JP-A 2008-147265 disclose other coil devices each of which comprises three or more pin lines but is of the vertical type. Therefore, the coil device of JP-A 2000-150258 or JP-A 2008-147265 is difficult to have a low-profile with multiple coils, as mentioned above.